Long time ago on a demonstration by the piano tuner Albert Ketentzian a 440Hz tone was played on an amplifier.
As the volume knob was turned clockwise the pitch decreased.
The explanation offered was that the harmonic distortion of the amplifier ie 880Hz which is a bad octave to our brain and therefore the brain now perceives the fundamental lower than 440Hz!
The explanation offered by Albert Ketentzian is an interesting one.
In fact this also happens without an amplifier, using just a tuning fork. (See Sound and Hearing - SS Stevens).
Does this sujest the nonlinearity of the ear brain as the cause?
Non linearity may shift the point at the basilar membrane in the same way that nonlinearity detects audio from rf AM radio waves as a shift in the DC point of a detecting electron tube, diode, or triode.
Do both phenomena of the title have a common explanation? Does the brain use the decrease in pitch as an electronic compressor amplifier sidechain signal to understand how loud a sound is and decrease its sensitivity?
Experimenting with a Casio MT-100 and playing the lowest F and then the highest shows that both notes sound lower in pitch when the volume is changed from quiet to loud.
Much more experimentation and a new theory would be nice.
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